Electrically operated hammer drill

ABSTRACT

A boring tool, axially reciprocable in a rotary chuck under repeated blows of a striker, is rotatable at either of two speeds from an electric motor by way of a transmission which includes two gear trains alternately made effective in two limiting positions of an axially shiftable coupling shaft. In an intermediate position of that shaft, the chuck is disengaged from both gear trains. The low-speed train includes a yieldable safety clutch to decouple the chuck from the motor in the case of overload.

ie States atent 1191 iersaclt Feb. 26, 1974 [54] ELECTRICALLY OPERATED HAMMER 3,203,490 8/1965 McCanty et a1. 173/1 17 DRILL 3,430,709 3/1969 Miller 173/1 17 [75] Inventor: Horst Biersack, Ansbach, Germany FOREIGN PATENTS OR APPLICATIONS 1,289,800 2/1969 Germany 173/104 1 Asslgnee- 221 3;? GmbH Ansbach 12,305 11/1956 Germany 173/104 [22] Filed: Sept. 16, 1970 Primary Examiner-James A. Leppink [21] pp NO 72 779 Attorney, Agent, or Firm-Karl F. Ross; Herbert u Dubno [30] Foreign Application Priority Data [57] ABSTRACT Sept. 23, 1969 Germany P 19 48 055.8 A boring tool, axially reciprocable in a rotary Chuck [52] Us Cl. 173/104 173/] 17 under repeated blows of a striker, is rotatable at either [51] lm'cl B25d 11/00 of two speeds from an electric motor by way of a [58] Fieid "i 1 l7 transmission which includes two gear trains alternately made effective in two limiting positions of an axially hiftable cou lin shaft. In an intermediate osition of [56] References Cited 8 p g p that shaft, the chuck 1s dlsengaged from both gear UNITED STATES PATENTS trains. The low-speed train includes a yieldable safety l,338,(ll9 4/l920 .lfiCkSOIl l73/l l7 clutch to decouple the chuck from the motor in the 1,617,025 2/1927 Nakayamo... 173/117 Case f overload 1,968,055 7/1934 Phillips 173/104 2,285,702 6/1942 Forss 173/104 10 Claims, 3 Drawing Figures PATENTEDFEBZSISH Sn'rEI l U? 3 In venlor:

Horst BIERSACK Attdrne PATENTED FEBZ 81974 SHEET 2 [1F 3 Fig. 2

In van/0r Horst BIE RSACK U Kpss Attorney Horst BIERSACK I v' i TI,

M Attorn SHEET 3 3 PATENTED FE82 6 I974 ELECTRICALLY OPERATED HAMMER DRILL My present invention relates to an electrically operated hammer drill having a tool casing or chuck, which is to be rotatably driven by an electric motor by means of a gear unit provided with a coupling means, and a striker member arranged to beat on a tool inserted in the casing.

In known sledge-hammer drills of this type, the tool liner or casing can be driven only at one rotary speed; the coupling means, which is operated from outside the drill, merely serves to switch on or off the rotary motion of the casing. Adjustments of the speed of rotation of the tool casing to suit the various tools which can be received therein, particularly with reference to the sizes of the tools and the purposes for which they are to be used, are thus not possible.

The invention is therefore concerned with the provision of an improved hammer drill of the type mentioned above in which this disadvantage is overcome and in which a simple manual control allows a rapid adjustment of the driving speed of the tool chuck, even during rotary impact operation, and which moreover permits, without the expense of any additional measures, disconnection of the rotary drive in the case of an electric motor running permanently during use of the drill.

In accordance with the invention, the transmission inserted between the tool holder and its drive motor is a two-spaced unit whose coupling means has a middle position, between the two selectively engageable gear speed, in which the rotary drive of the tool casing is disengaged. the

In this way, a sledge-hammer drill is obtained wherein the tool holder or casing can be driven at ei-- ther of two different speeds with a neutral position therebetween, so that, for example, with smaller or thinner tool bits greater speed and greater thrust can be used, thereby resulting in shorter periods of operation. Furthermore, by using an increased speed in the case of correspondingly shaped percussion-drill inserts, a better removal of th chips and thus also a better drilling quality is obtainable. Also, drilling in steel or other materials is improved by the various speeds. The striker mechanism can moreover be operated on a shorter working stroke.

In order to ensure satisfactory coupling and a longer service life for the transmission or gears unit, there is provided a coupling shaft which is permanently connected with an externally toothed part of the tool casing by way of a pinion, and which is axially adjustable by an external control device or gear shifter. The shaft is provided with two clutch members firmly mounted thereon, which can be selectively brought into and out of engagement with coacting clutch members arranged one on each side thereof and connected with gearwheels of two gear trains that are, in permanent driving connection with the motor shaft and freely rotatable on the coupling shaft. This means that all the gearwheels of the gear unit are constantly engaged so that varying side stresses are avoided whereas only two clutch memhere or rims, which are sufficient for the greatest operating stresses, are brought into and out of engagement with corresponding coacting couplings whereby the clutch engagements and disengagementscan be carried out even during drilling by a simple manual operation on an external gear shifter or control handle which is easy to manipulate.

According to a further feature of the invention, an intermediate shaft supported at both ends is arranged between the motor shaft and the coupling shaft and carries a sleeve provided with a pair of external sets of teeth, the sleeve being entrainable by the intermediate shaft through the intermediary of a yieldable safety clutch. In this arrangement, one of the external sets of teeth of the sleeve permanently meshes with the motor shaft and the other set of teeth permanently meshes with one of the gearwheels freely rotatable on the coupling shaft, thereby forming one gear train. The other gearwheel which is freely rotatable on the coupling shaft is in constant engagement with a gearwheel which is secured to the intermediate shaft, thereby forming the second gear train.

In order to achieve a compact construction and to ensure a uniform bearing load and a small torque acting on the shaft, the two pairs of gearwheels respectively forming the two gear trains are arranged directly adjacent the two support bearings for the intermediate and coupling shafts, whereas the externally toothed sleeve portion which mates with the motor shaft is located approximately in the middle of the intermediate shaft, the two coupling rims being attached to the coupling shaft on opposite sides of the layer diameter set of teeth which is in permanent mesh with or driving pinion of the motor.

One end of the coupling shaft is acted upon by a spring-loaded thrust bearing and the other carries a bearing pin which is freely rotatable therein and rigidly connected with an end plate which is non-rotatable and axially displaceable within limits set by a longitudinal slot of the housing. The end plate of the bearing pin abuts an eccentric cam which is actuated by the external control knob or handle through a pivot pin which extends at right angles to the coupling shaft in the housing of the hammer drill and is indexable by a springloaded detent pin.

By way of example, an embodiment of the invention is described below and illustrated in the accompanying drawing, in which:

FIG. 1 is a mainly sectional side view of the front part of a hammer drill according to the invention;

FIG. 2 is a sectional front view of the hammer drill, with the front part of the housing removed, taken along the line II-"II of FIG. 1; and

FIG. 3 is a plan view of the hammer drill of FIG. 1 partly broken away to exposed a gear-shift mechanism operable by an external control handle.

The illustrated hammer drill embodying the invention has a housing 1 consisting essentially of four parts 1', ll", 1" and l which are screwed together. A tool chuck or casing 2, a coupling shaft 3, an ancillary or intermediate shaft 4 and a motor shaft 5 are arranged one beneath the other in the housing 1. The motor shaft 5, which is driven by an electric motor 5', is mounted in a bearing 5" and extends from the motor beyond the bearing, the projecting front part 5" of the shaft being formed as a pinion, in permanent engagement with a set of external gear teeth 6a on a sleeve 6', the latter being coupled with ancillary shaft by way of a releasable safety clutch 6, which consists essentially of a plurality of coupling pins 6" in a hub 6'V firmly connected with the intermediate shaft 4, the coupling pins being acted,upon by radial springs 6". The intermediate shaft is journaled at its ends in bearings 4 and 4", a gearwheel 7 located directly adjacent the bearing 4 being secured to the shaft for joint rotation; a gearwheel 8, which is nonrotationally connected with the outermost end of the toothed sleeve 6' of the safety clutch 6 by means of a fitting 8, is mounted directly adjacent the bearing 4".

The coupling shaft 3 is journaled at its ends in bearings 3 and 3" and carries, directly adjacent the bearing 3, a gearwheel 9 which is freely rotatable thereon. Directly adjoining the bearing 3 there is located on the shaft 3 a gearwheel 10 which is also freely rotatable on the shaft and meshes with another set of external gear teeth 6b on sleeve 6'. These two freely rotatable gearwheels 9 and 10 are provided with clutch elements 9, 10', respectively, which co-operate respectively with coacting clutch elements in the form of annular dog or claw couplings 11, 12 which are firmly secured to the coupling shaft 3. The end of the coupling shaft 3 facing the bearing 3" abuts a ball bearing 13 which is constantly biased toward the left by a compression spring 14. This end of the shaft is received in the gearwheel 10 which is journaled in turn in the bearing 3" by means of a tubular extension of the gearwheel. The other end of the shaft 3 extends through the bearing 3, and terminates in a pinion 3". This end of the shaft 3 supports a bearing pin 15 which is freely rotatable therein and firmly connected with an end plate 15' which is non rotatable and axially displaceable within limits set by a longitudinal slot 1" of the housing portion 1'. The end plate 15 also abuts an eccentrically mounted cam 17, which is operated by an external control handle 16 (see FIG. 3). The pinion 3 of the coupling shaft 3 mates with the rear (right hand) end of the tool chuck or casing 2 which is formed as a gearwheel 2'. All the drilling tools which are required for each operation are placed in the tool casing 2.

As can best be seen from FIG. 3, the cam 17 is fastened to a pivot pin 17' which extends at right angles to the coupling shaft 3 in the housing part 1' and whose polygonal central portion 17"abuts a detent pin 18 which moves under the action of a spring 18" whose pressure can be adjusted by a screw 18. The pivot pin 17' supports an external knob 16 on the end thereof which projects laterally out of the housing section 1'.

During hammering, a percussion piston 20 which moves in a guide cylinder 19, is set in oscillatory motion by means of a piston rod 21, which is likewise driven by an electric motor and which is not illustrated in further detail, and, by way of an air cushion 22, drives a striking anvil 23, which likewise moves in the guide cylinder 19, in oscillating strokes to the rear end of a tool 24 inserted in the tool casing 2. At the same time, with the coupling shaft 3 in gear, the tool casing 2 is set in rotation by the meshing of its toothed rim 2 and the pinion 3" of the coupling shaft 3. Thus, through suitable adjustment of the external gear shifter 16 acting by way of the pivot pin 17' and the cam 17, the coupling shaft 3 can be so displaced that either the coupling rim 11 comes into engagement with the coacting clutch element 9 of the gearwheel 9 or the coupling rim 12 engages with the coacting clutch element 10' of the gearwheel 10, whereby the tool case 2 can be driven at different speeds. If on the other hand the coupling shaft 3 is set by the controller 16 in its neutral middle position illustrated in FIG. 1, the two coupling rims l1, 12 both move out of engagement with the clutch elements associated with the gearwheels 9, 10, whereby the rotary drive for the tool case 2 is interrupted. To this end, it is essential that the gearwheels 9, l0 and the coupling rims 11, 12 are so arranged that between the disengagement of one gearwheel, for example gearwheel 9 and the engagement of the other, for example gearwheel 10, there is room for the intermediate neutral position.

The loading spring 14 and ball bearing 13 keep the coupling shaft 3 and the end plate 15 rotatably positioned therein in permanent contact with the eccentric cam 17 of the pivot pin 17 which is in turn retained by the detent pin 18 in one of its three different shifting positions. The coupling shaft 3 is thus held in an operative position establishing either of the two available speed ratios, or in the neutral position located thercbetween. The toothed extremity 3 of shaft 3 is long enough to remain in mesh with gear teeth 2' in any of these positions.

As can be seen from FIG. 1, in the embodiment illustrated the safety clutch 6 is associated with the more slowly rotating gear train 7, 9 which supplies the greater torque, but does not act on the gear train 8, 10, which as a rule regains no such overload protection by means of its greater driving speed and the correspondingly smaller torque transmitted thereby. It is obvious, however, that such an overload clutch may also be provided for both gear drives. Furthermore, instead of providing the special coupling rims 11, 12 rigid with shaft 3 and the coacting formations 9', 10' rigid with gears 9 and 10, I may move the gearwheels 9, l0 closer together and firmly attach them to coupling shaft 3 so that they can then be selectively brought into direct engagement with the associated gearwheels 7, 8 or, with the coupling shaft 3 in the middle position, be disengaged therefrom.

I claim:

1. A hammer drill comprising:

a housing;

a chuck journaled in said housing for rotation about an axis with entrainment of an axially reciprocable boring tool;

axially oscillatable striker means in said housing aligned with said chuck for reciprocating said tool along said axis;

a drive motor supported by said housing;

transmission means linking said motor with said chuck for rotating said tool, said transmission means including a gear carrier shiftable parallel to said axis between a first limiting position establishing a first speed ratio, a second limiting position establishing a second speed ratio and an intermediate position disconnecting said motor from said chuck; and

control means on said housing for selectively moving said coupling means into any of said positions.

2. A hammer drill as defined in claim 1 wherein said gear carrier comprises a coupling shaft parallel to said axis in permanent driving engagement with said chuck, said transmission means including first and second gears permanently coupled with said motor for rotation thereby and alternately effective in said first and second limiting positions to drive said coupling shaft.

3. A hammer drill as defined in claim 2 wherein said first and second gears are part of respective gear trains dimensioned to drive said coupling shaft at a relatively low speed and a relatively high speed, at least one of said gear trains including yieldable clutch means for decoupling said chuck from said motor in the case of overload.

4. A hammer drill as defined in claim 3 wherein said one of said gear trains is the one driving said coupling shaft at said relatively low speed.

5. A hammer drill as defined in claim 4 wherein said transmission means comprises an ancillary shaft and a sleeve thereon coupled with said ancillary shaft by said clutch means for joint rotation, said motor being provided with a driving pinion, said sleeve having a first set of gear teeth in mesh with said pinion and a second set of gear teeth forming part of said gear train, said first gear train including a gearwheel mounted directly on said ancillary shaft for rotary entrainment thereby.

6. A hammer drill as defined in claim 5 wherein said first and second gears respectively mesh with said gearwheel and with said second set of gear teeth, said ancillary shaft being parallel to said coupling shaft.

7. A hammer drill as defined in claim 6 wherein said first set of gear teeth has a diameter larger than that of said second set and is located between said first and second gears.

8. A hammer drill as defined in claim 6 wherein said first and second gears are freely rotatable on said coupling shaft and are provided with first and second coupling formations respectively rigid therewith, said coupling shaft carrying coacting means respectively engageable with said first and second formations in said first and second limiting positions while being disengaged therefrom in said intermediate position.

9. A hammer drill as defined in claim 2 wherein said control means comprises a rotatable member on said housing and a in rigid with said member perpendicular to said coupling shaft, said pin being provided with cam means engaging said coupling shaft for axially shifting same.

10. A hammer drill as defined in claim 9 wherein said coupling shaft is provided at one end with a springloaded thrust bearing and with abutment means on the other end engaged by said cam means, said pin being provided with indexing means for retaining said cam means in a selected position against the axial thrust of 

1. A hammer drill comprising: a housing; a chuck journaled in said housing for rotation about an axis with entrainment of an axially reciprocable boring tool; axially oscillatable striker means in said housing aligned with said chuck for reciprocating said tool along said axis; a drive motor supported by said housing; transmission means linking said motor with said chuck for rotating said tool, said transmission means including a gear carrier shiftable parallel to said axis between a first limiting position establishing a first speed ratio, a second limiting position establishing a second speed ratio and an intermediate position disconnecting said motor from said chuck; and control means on said housing for selectively moving said coupling means into any of said positions.
 2. A hammer drill as defined in claim 1 wherein said gear carrier comprises a coupling shaft parallel to said axis in permanent driving engagement with said chuck, said transmission means including first and second gears permanently coupled with said motor for rotation thereby and alternately effective in said first and second limiting positions to drive said coupling shaft.
 3. A hammer drill as defined in claim 2 wherein said first and second gears are part of respective gear trains dimensioned to drive said coupling shaft at a relatively low speed and a relatively high speed, at least one of said gear trains including yieldable clutch means for decoupling said chuck from said motor in the case of overload.
 4. A hammer drill as defined in claim 3 wherein said one of said gear trains is the one driving said coupling shaft at said relatively low speed.
 5. A hammer drill as defined in claim 4 wherein said transmission means comprises an ancillary shaft and a sleeve thereon coupled with said ancillary shaft by said clutch means for joint rotation, said motor being provided with a driving pinion, said sleeve having a first set of gear teeth in mesh with said pinion and a second set of gear teeth forming part of said gear train, said first gear train including a gearwheel mounted directly on said ancillary shaft for rotary entrainment thereby.
 6. A hammer drill as defined in claim 5 wherein said first and second gears respectively mesh with said gearwheel and with said second set of gear teeth, said ancillary shaft being parallel to said coupling shaft.
 7. A hammer drIll as defined in claim 6 wherein said first set of gear teeth has a diameter larger than that of said second set and is located between said first and second gears.
 8. A hammer drill as defined in claim 6 wherein said first and second gears are freely rotatable on said coupling shaft and are provided with first and second coupling formations respectively rigid therewith, said coupling shaft carrying coacting means respectively engageable with said first and second formations in said first and second limiting positions while being disengaged therefrom in said intermediate position.
 9. A hammer drill as defined in claim 2 wherein said control means comprises a rotatable member on said housing and a in rigid with said member perpendicular to said coupling shaft, said pin being provided with cam means engaging said coupling shaft for axially shifting same.
 10. A hammer drill as defined in claim 9 wherein said coupling shaft is provided at one end with a spring-loaded thrust bearing and with abutment means on the other end engaged by said cam means, said pin being provided with indexing means for retaining said cam means in a selected position against the axial thrust of said bearing. 